[krisoft]

Detecting gravitational waves requires extreme precision. Pastries are in the ordinary precision range. :)

Joking aside I suspect if you are good enough where the limiting factor in your baking is the precision of butter specified as opposed to sloppy techniques you are better off using a recipe written by a professional pastry chef for other proficient bakers. In my experience they usually write quantities in terms of weight and recommend measuring it that way.

For example Claire Saffitz calls in her Confetti Cake recipe for "3 sticks unsalted butter (12 oz / 340g), at room temperature". That would indicate that the 100g approximation is 13% low.